The modern athletic shoe is a highly refined combination of many elements which have specific functions, all of which must work together for the support and protection of the foot during athletic activity and events. A shoe is divided into two general parts, an upper and a sole.
The upper is designed to snugly and comfortably enclose the foot. Typically, an upper of an athletic shoe will have several layers including a weather- and wear-resistant outer layer of leather or synthetic material such as nylon, and a soft, padded inner liner for foot comfort. Current athletic shoe uppers typically have an intermediate layer of a synthetic foam material. The three layers of the upper may be fastened together by stitching, cementing, or a combination of these. In areas of maximum wear or stress, reinforcements of leather and/or plastic are attached to the upper. Examples of such reinforcements are leather toe sections attached over synthetic inner layers of the toe area and heel counters made of an inner layer of plastic and an outer layer of leather.
The other major portion of an athletic shoe is the sole. Designed to withstand many miles of running, it must have an extremely durable bottom surface to contact the ground. The ground contact surface of an athletic shoe includes traction elements or cleats to enhance the traction between the foot and the ground. The considerable forces generated by running require that the sole of a running provide enhanced protection and shock absorption for the foot and leg. Accordingly, the sole of a running shoe typically includes several layers, including a resilient, energy-absorbent material as a midsole and a ground contacting outer sole or outsole, which provides durability, cushioning and traction. This is particularly true for a training or jogging shoe designed to be used over long distances and over a long period of time. The sole also provides a broad, stable base to support the foot during ground contact. In the design and construction of prior art outer soles for athletic shoes, traction and durability have been the primary factors given consideration. While these factors are important, other performance factors, such as light weight, flexibility, and enhanced foot dynamics also merit emphasis. Moreover, since the outer sole constitutes about 1/3 of the total weight of the shoe, it is important to maximize its contribution to comfort, performance, support and protection of the foot.
The broad concept of using cleats and ridges for improved traction and comfort in a running shoe are disclosed in the prior art. For example, U.S. Pat. No. 4,364,190 issued to Ronald C. Yonkers on Dec. 21, 1982 discloses an outer sole for an athletic shoe wherein a plurality of bars extend downward from the base of the outsole in a transverse direction, and the widths of the bars are varied in proportion to the load exerted on the outsole at various longitudinal locations. The use of transverse bars enhances flexibility and provides lateral stability, while varying the width of the bars provides traction and wear resistance where necessary and keeps the weight of the outsole relatively low.
U.S. Pat. No. 4,262,435 issued to Block et al. on Apr. 21, 1981 discloses an athletic shoe wherein the sole piece has a flexure break segment of reduced thickness. The reduced thickness break segment follows and underlies the phalangal-metatarsal joint line. The reduced thickness break segment thus is formed as a single line extending across the width of the sole piece, with the line having two segments disposed at different angles with respect to a lengthwise direction of the sole. These segments join at a point intermediate the transverse width of the sole piece. The U.S. Pat. No. 4,262,435 patent states that the flexibility of the sole piece is enhanced along the length of the reduced thickness break segment. However, a resistance point is created where the two segments of the break are joined in the interior area of the sole. Thus, while the U.S. Pat. No. 4,262,435 patent recognizes the desirability of enhancing the flexibility of a sole piece to accommodate the natural motions of the foot, the particular technique disclosed in the patent does not accomplish this objective in an optimal manner.